(i) Field of the Invention
This invention relates to a process for the treatment of protein solutions.
(ii) Description of the Prior Art
Whey proteins are commonly concentrated through the use of ultrafiltration. However, attempts to utilize membranes in processes which require the protein to permeate through the membrane [e.g., microfiltration (MF) for bacterial removal or selective fractionation of proteins by ultrafiltration (UF)] have been less successful. Standard organic membranes in spiral or flat sheet format exhibit soiling which may be partially due to the formation of a secondary membrane layer resulting in the rejection of proteins sized well below the molecular weight cut off (MWCO) for that membrane. For example, beta-lactoglobulin (MW: 18,000) which exists as a dimer in whey (MW: 36,000) exhibits significant rejection on membranes with much higher MWCO including even MF membranes. This fact has been used as the basis for concentrating beta-lactoglobulin relative to alpha-lactalbumin (MW: 14,000) (see U.S. Pat. No. 5,008,374).
The problem of protein rejection can be controlled in tubular membrane systems through the use of inorganic membranes employing high product recirculation rates and mechanisms to minimize transmembrane pressure which may include cocurrent circulation of permeate. This approach is characterized by high capital and operating costs and is limited to microfiltration applications.